Modern endodontic treatment involves removal of the damaged pulp, followed by cleaning and shaping of the root canal space, irrigating, and filling with biocompatible material such as gutta-percha and a root canal sealer.
Shaping of the canal is performed either manually, using a series of stainless steel hand-held files, or mechanically, using rotary nickel-titanium files adapted to fit a standard or dedicated dental handpiece.
The manual process relies on the experience of the dentist, is physically difficult to perform and is time-consuming. The use of files requires repeated changing between numerous different rat-tail files, progressively increasing from the smallest to the largest. Its reach to the apical constriction for widening and removal of the smear layer is limited. The reason for such limitations relates to the moderate elasticity of the steel files and the risk of fracture when excessive force is applied.
Although the field of elastic rotary nickel-titanium endodontic files has developed greatly over the last few years, fracture (separation) of nickel-titanium rotary files is still often reported, and hence the use of such is restricted. In order to overcome the fracture problem, a large range of dedicated handpiece systems, powered by slow speed transaction equipped with torque and speed control limitation circuits, have been developed, requiring a high level of professional skill for their operation. As a result, the cost of files and the related equipment per endodontic treatment has increased and instruments are typically operated only by experts in the endodontic field, while non-specialists use standard handpieces in a risky procedure.
Additionally the round cross-section of the file prevents adequate cleaning when the canal cross-section is oval or narrow in shape. In such cases, enlargement of the canal cross-section to accept the round cross-section of the file, may weaken or perforate the wall or the apical portion of the canal. The same risk of perforation applies in case of a curved root canal, where the file tends to follow the path of least resistance, acting rigorously on the convex walls within the reach of the file, and insufficiently over the concave portions.
US20070099149 entitled “Endodontic device and method of utilizing and manufacturing same” corresponding to IL 171705 in the name of the present applicant discloses an endodontic device for cleaning, filing or reaming root canals. The device includes one or more metallic, flexible strands having an edge, a working section, a connecting section and a coupling head connected thereto. The strands are coated along the working section with a thin layer of a binder having abrasive particles embedded therein. The flexible, longitudinal strands are so constructed that their outer surfaces serve as active filing surfaces.
In operation the strand section of the endodontic file is inserted into the root canal to the apex, and the strand or strands are mechanically rotated by a handpiece to a high speed. The thin, flexible portion of the device is centrifugally thrown against the canal wall following the natural curvature and complex cross-section of the root canal in exact manner. The whole contents of US20070099149 are incorporated herein by reference.
WO2008/102321 entitled “Endodontic file” corresponding to IL 181439 in the name of the present applicant and likewise incorporated herein by reference, teaches an endodontic file comprising at least one cord and a wire wound around at least a major portion of the cord, the wire having an abrasive outer surface.
WO/2011/104705 entitled “Rotary Endodontic File with Frictional Grip” corresponding to IL 204195 filed in the name of the present applicant and likewise incorporated herein by reference, teaches an endodontic file similar to that described in WO2008/102321 but having an elastomeric grip partially covering the helically wound wire near a first end thereof and having an outer diameter that is slightly wider than an internal diameter of a barrel of a dental instrument whereby on insertion into the barrel it is supported therein only by friction.
Conventional endodontic reamers are hand-held but the reamers described in the above-referenced publications are configured for rotation at low speed by an electrical motor. By “low-speed” is meant less than 40,000 rpm as distinct from the “high-speed” of 300,000-40,000 rpm at which dental drills are rotated. It will be appreciated that the terms “low” and “high” in this context are relative since a rotation speed of 30,000 rpm is certainly “high” compared to conventional manual reamers. To this end, the reamers in all of the above-referenced publications include a central cord around a major portion of which there is wound a wire having an abrasive outer surface. In practice, the central cord comprises not a single low gauge (i.e. high diameter) wire but rather a plurality of high gauge (i.e. low diameter) wires that are twisted together to afford high flexibility, which is obviously important in root canal treatment. In order to prevent the wires from untwisting during treatment, the tips of the wires are welded to form a hemi-spherical bulb that takes no part in the root canal procedure other than to prevent the free ends of the wires from untwisting. The hemi-spherical bulb also ensures that tip of the file does not damage the inner wall of the root canal on contact therewith and helps to reduce the likelihood of the file sticking against an inner surface of the root canal, even though this cannot be entirely prevented.
In order to accommodate undesirable sticking, which could result in breakage of the endodontic file, WO/2011/104705 limits the transmitted torque by employing a friction grip that allows the tool to slip within its coupler.
Current solutions for rotary preparation are based on different types of Nickel-Titanium files. The level of skill required by the dentist is high, and the supplies are expensive thus ruling out use of such files for all but a small fraction of practitioners. Moreover, notwithstanding the improvements to endodontic files contemplated by the above-referenced prior art, shaping of the root canal still requires use of multiple files, resulting in root canal treatment being tedious for the dentist and uncomfortable for the patient.
It would therefore be desirable to simplify root canal preparation while avoiding the weaknesses of existing products leading to file breakage, perforations, ledging, and penetration of the periapical tissue. It is also desirable to reduce the treatment time, compared to current endodontic files and procedures.